Respirators are devices that protect workers and others from harmful health effects associated with airborne hazards. The devices are worn about the face, acting to remove unwanted contaminants from the breathing air supply. The contaminants may be solid particles such as fumes, bioaerosols, or other particles, or they may be gasses or vapors, or combinations of such substances.
Respirators come in a variety of shapes and forms and are commonly designed according to the wearer's protection needs. Respiratory products range from simple filtering facepieces, typically referred to as dust masks, to more sophisticated systems that use an elastomeric facepiece in connection with one or more replaceable filtering cartridges. Some respiratory devices additionally employ a blower to assist in delivering a clean air supply to the wearer. These products typically are referred to as positive pressure respirators or powered air purifying respirators.
A variety of different filter cartridge designs have been developed over the years for use with respiratory masks. Typical filter cartridges contain a filter medium of active particulate disposed within a housing. Some designs have used packed beds of activated carbon in metal canisters—see for example, U.S. Pat. No. 4,543,112, or between support plates—see U.S. Pat. No. 7,419,526B2 to Greer et al. Other cartridges have used injection molded plastic housings—see, for example, U.S. Pat. Nos. 5,078,132 and 5,033,465 to Braun et al.—to contain the active particulate, which may be held together by bonding components—see also U.S. Pat. No. 5,952,420 to Senkus et al. and U.S. Pat. No. 6,216,693 to Rekow et al. In a more recent design, the investigators have described the use of a thermoformed housing to reduce overall cartridge weight—see U.S. Pat. Nos. 7,497,217 and 6,874,499 to Viner et al. Even though overall weight may be reduced with a thermoformed housing, known filter cartridges, which have used metal or plastic housings, have still had to contend with the added weight that comes with the complete housing structure. The typical filter cartridge also has not provided a dual flow pattern to reduce pressure drop across the filter media. Although bifurcated or dual flow cartridges also have been developed, which contain two spaced layers of filter media separated by a central plenum—see U.S. Pat. Re 35,062 to Brostrom et al.—these dual flow products, however, have not had a housing sidewall that defines the cartridge perimeter. As a result, the dual flow cartridges have generally contained lower volumes of filter media, which has placed limits on filter cartridge service life. Known filter cartridge products therefore have been confronted with a weight versus service life contest, which the present invention, as discussed below, addresses.